Geometric Model, L. Brill No. 166. Ser. 13 No. 4, Ruled Surface with Two Conjugated Imaginary Double Lines

Geometric Model, L. Brill No. 166. Ser. 13 No. 4, Ruled Surface with Two Conjugated Imaginary Double Lines

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The German Karl Rohn (1855-1920) intended to become an engineer, but found the mathematical part of his studies at the polytechnic in Darmstadt more intriguing. He studied mathematics with Alexander von Brill and Felix Klein in Munich, and went on to a career as a professor of mathematics in Leipzig and Dresden.
In 1886 and again in 1892, Rohn published sets of string models with the publisher and mathematical model distributor Ludwig Brill. Several models from the first set, Brill’s Series XIII, were exhibited at the Columbian Exposition, a world’s fair held in Chicago in 1893. This is one of them, number 4 in the series.
The thread model has a metal frame. It shows two congruent hyperboloid-like ruled surfaces (in gold), and a vertical straight line that runs between them (in red).
The model was received at the Smithsonian with one bit of thread and restrung.
L. Brill, Catalog mathematischer Modelle..., Darmstadt: L. Brill,1892, pp. 27-28, 68.
“Mathematical Models of Surfaces,” University of Groningen, website accessed October 16, 2017. This site describes the mathematics of these surfaces in more detail. It illustrates them with examples of the models published by Brill’s successor, Martin Schilling - still as series XIII.
Currently not on view
Object Name
Geometric Model
geometric model
date made
L. Brill
place made
Germany: Hesse, Darmstadt
Physical Description
string (overall material)
metal (overall material)
overall: 19 cm x 18 cm x 18 cm; 7 15/32 in x 7 3/32 in x 7 3/32 in
ID Number
catalog number
accession number
Credit Line
Gift of Wesleyan University
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Medicine and Science: Mathematics
Science & Mathematics
Data Source
National Museum of American History
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